The Supreme Court denied the petition about an hour before the scheduled execution, according to Sells' lawyers.

Several death row inmates have challenged their executions because states would not disclose which compounding pharmacies supplied the chemicals. The Court has yet to prevent a lethal injection on those grounds.

States have been forced to use less-regulated compounding pharmacies for the specially-mixed drugs because the manufacturers have refused to sell the products for executions, and they are anxious to protect the businesses' anonymity.

"TDJC legitimately believes that disclosing the identity of the pharmacy will create a substantial risk of physical harm to the pharmacy and its employees, based on specific bomb threats delivered to a similarly situated pharmacy which planned to supply drugs for use in executions," the state said in its reply to the Supreme Court petition.

Defense lawyers contend that they can't challenge the drugs on the grounds that they would cause an excruciating death — in violation of the constitutional protection against cruel and unusual punishment — if they don't know where they're coming from or how they're prepared.

Texas says it has enough pentobarbital to carry out all five scheduled executions in April and May, starting with Sells, who was convicted of murdering Kaylene Harris, the daughter of an acquaintance, in 1999.

Armed with a butcher knife, he tried to molest the sleeping Kaylene and then stabbed her 16 times — slitting her throat several times — when she tried to escape. He then slit the throat of a friend who was sleeping in the top bunk before fleeing. She survived.

Sells subsequently claimed to have committed as many as 70 murders during two decades as a drifter, though authorities have not corroborated those claims.